Support feather board, move to broken out source

src/edmfd/mcp23017.hh

@@ -0,0 +1,31 @@
+#pragma once
+
+namespace mcp23017 {
+
+enum class reg : uint8_t {
+    iodira, iodirb,
+    ipola, ipolb,
+    gpintena, gpintenb,
+    defvala, defvalb,
+    intcona, intconb,
+    iocona, ioconb,
+    gppua, gppub,
+    intfa, intfb,
+    intcapa, intcapb,
+    gpioa, gpiob,
+    olata, olatb,
+};
+
+class gpios
+{
+public:
+    gpios(uint8_t addr);
+
+    int read(reg r, uint8_t *value);
+    int write(reg r, uint8_t value);
+
+private:
+    uint8_t m_addr;
+};
+
+} // namespace mcp23017